1. Field of the Invention
The present application relates to a polymeric material and to a method for production thereof.
2. Description of the Prior Art
Heretofore, polymeric materials in the form of membranes have found utility in a range of industrial applications including, for example, technologies such as reverse osmosis, ultrafiltration, pervaporation and electrolysisxe2x80x94see Synthetic Membranes and Membrane Separation Process (Matsuura), CRC Press: Boca Raton, 1993.
More recent applications of this technology have been directed to the production of membranes with substantially uniform pores sizes to be used as templates for nanomaterial fabricationxe2x80x94see any of Science 1994, 266, 1961 (Martin); Chem. Mater. 1996, 8, 1739 (Martin); Science 1995, 268, 700 (Nishizawa et al); and Science 1995, 270, 68.
To date, the prior art has attempted a number of approaches for producing polymeric membranes comprising relatively small pores.
These approaches include quenching the morphology of a solvent-swollen polymer film by the sudden immersion thereof in a poor solvent or the thermal quenching of a polymer film stretched at a higher temperaturexe2x80x94see Synthetic Membranes and Membrane Separation Process (Matsuura), CRC Press: Boca Raton, 1993. In essence, the pores in the resulting polymeric membranes are kinetically xe2x80x9cfrozenxe2x80x9d in a matrix and the performance of the polymeric membrane is very sensitive to minor variations in the processing conditions.
U.S. Pat. No. 5,425,865 [Singleton et al.] relates to a composite polymer membranexe2x80x94see column 1, lines 6-9. The polymer membrane comprises a first polymeric material providing a porous matrix and a second polymeric material which at least partially fills and thereby blocks the pores of the matrix, at least one of the two polymeric materials (preferably both) being cross-linkedxe2x80x94see column 2, lines 47-53. The process to produce the subject polymeric membrane is based on initially providing the first polymeric material having the porous matrix incorporated thereinxe2x80x94see column 2, lines 54-66.
U.S. Pat. No. 5,342,521 [Bardot et al.] relates to a reverse osmosis or nanofiltration membrane usable in the agroalimentary and pharmaceutical industriesxe2x80x94see column 1, lines 5-8. The subject membrane comprises a laminate structure made up of: (i) an inorganic material porous support; (ii) a first inorganic material mesoporous layer having a mean pore radius below 10 nm coated on (i); and (iii) inorganic mineral polymer or organic polymer second active layer placed on (ii) and having a prescribed thicknessxe2x80x94see column 2, lines 5-15.
U.S. Pat. No. 5,238,613 [Andersen] relates to polymeric, microporous membrane materials characterized by a continuous, triply-periodic, highly branched and interconnected porous space methodology having a globally uniformed, pre-selected pore sizexe2x80x94see column 2, lines 62-66. The subject membrane can be produced by xe2x80x9cchemical erosionxe2x80x9d or xe2x80x9cchemical degradationxe2x80x9d in one component of a block copolymerxe2x80x94see columns 6, lines 54-59 and column 8, lines 5-12. This approach is discussed in more detail at column 14, line 19 to column 16, line 58. This excerpt of the reference makes it relatively clear that the porous structure is achieved by complete degradation of a susceptible block in the block copolymer resulting in scission of the polymer backbone. Examples of such degradation include ozonolysis (column 15, lines 42-54), radiation (column 15, lines 55-65) and thermal decomposition (column 16, lines 20-24).
U.S. Pat. No. 5,130,025 [Lefebvre et al.] relates to a new highly permeable anisotropic synthetic membrane comprising a multi-layered structure (preferably 4-12 layers), with each layer serving as a molecular screen of precise molecular weightxe2x80x94see Abstract. Between each membrane layer are rows of alveolae with adjacent alveolae in adjacent rows being connected by means of channels of molecular dimensionsxe2x80x94see Abstract.
U.S. Pat. No. 5,066,401 [Mxc3xcller et al.] relates to a membrane based on two polymersxe2x80x94see column 1, lines 9-14. This membrane is modified to confer hydrophilic properties theretoxe2x80x94see column 2, lines 30-39. One approach by which hydrophilicity can be conferred to the membrane is to subject the membrane to chemical modification such as hydrolysis, transesterification and/or aminolysisxe2x80x94see column 6, line 1 to column 8, line 30. It is important to bear in mind that this reference teaches chemical modification for the sole purpose of conferring hydrophilicity to a membrane already having a porous structure.
U.S. Pat. No. 5,049,275 [Gillberg-LaForce et al.] relates to microporous membranes incorporating a vinyl polymer within the pores to result in modified properties of the membranexe2x80x94see column 1, lines 5-8. The approach in this reference is to start with a microporous membrane and incorporate and familiarize in the pores of the membrane a polymerizable vinyl monomerxe2x80x94see column 3, lines 26-37. The purported advantage of this approach is the ability to modify a hydrophobic microporous membrane with a hydrophilic monomerxe2x80x94see column 3, lines 47-52.
U.S. Pat. No. 5,028,335 [Sleytr et al.] relates to a structure comprising at least one membrane with continuous pores having a defined diameter rangexe2x80x94see column 1, lines 16-23. The purported advantage of the invention appears to be the ability to link foreign molecules with protein molecules or protein containing moleculesxe2x80x94see column 2, lines 55-56.
U.S. Pat. No. 4,923,608 [Flottmann et al.] relates to a flat membrane derived from sheets of organic polymers, glass or ceramic materials having a defined pore structure produced by erosion of the membrane material using one or more pulsed lasersxe2x80x94see column 1, lines 8-17.
U.S. Pat. No. 4,595,707 [McCreedy et al.] relates to microporous membranes comprised of a glassy polymer composition (optionally cross-linked) in a polymeric domain grafted to at least a portion of the porous structure of the membranexe2x80x94see column 2, lines 32-38. The approach here is to start with a membrane of the glassy polymer and subject that membrane to xe2x80x9ccrazingxe2x80x9d in the presence of monomers which are polymerizable with the polymer composition during crazing leading to formation of the microporous structurexe2x80x94see column 2, lines 17-31.
While the prior art approaches for production of polymeric membranes have met with a varying degree of success, the art is in need of a polymeric membrane having a porous structure, the pore dimension of which is xe2x80x9ctuneablexe2x80x9d to a particular application. In other words, it would be desirable to have a polymeric material, such as a membrane, which could be produced readily and precisely with a pre-selected pore dimension. It would also be desirable to have a polymeric material, such as a membrane, which could be produced with very small pores (e.g.  less than 50 nm).
Accordingly, in one of its aspects, the present invention provides a polymeric material comprising a microporous matrix disposed in a multi-block polymer having a backbone of the general formula:
[(A)nxe2x88x92(B)mxe2x88x92(X)l]p
wherein:
A is a first copolymerized monomer;
B is a second copolymerized monomer;
X is a third copolymerized monomer the same as or different from A;
n and m are the same or different and are each an integer in the range of from 30 to 3000;
l is 0 or an integer in the range of from 30 to 3000;
p is an integer in the range of from 1 to 100;
wherein the microporous matrix is defined by reactive cleavage of at least a portion of a pendant moiety on B.
In another of its aspects, the present invention provides a process for producing a polymeric material having a microporous matrix from a multi-block copolymer having a general formula: 
wherein:
A is a first copolymerized monomer;
B is a second copolymerized monomer;
X is a third copolymerized monomer the same as or different from A;
L is a leaving group, at least a. portion of which is cleavable;
n and m are the same or different and are each an integer in the range of from 30 to 3000;
l is 0 or an integer in the range of from 30 to 3000;
p is an integer in the range of from 1 to 100; the process comprising the steps of:
(i) cleaving at least a portion of L from the multi-block copolymer to produce polymeric material having an intact backbone; and
(ii) forming the microporous matrix in the multi-block copolymer at locations from which the at least a portion of L is removed from the multi-block copolymer.